MATLAB Answers

mr mo
0

Replacing same rows with same variables in first to third column

Asked by mr mo
on 21 Dec 2017
Latest activity Commented on by Stephen Cobeldick on 21 Dec 2017
Hi. I have two matrices named aa and m.
aa=[1 2 3 7
4 5 6 8
7 8 9 9
3 2 3 8
6 5 6 7
7 8 7 9];
mm=[1 2 3 5
4 5 6 9
7 8 9 6];
I want to replace the rows of aa with the rows of m that have the same values in first to third column.
How can I do that?
Thanks a lot.

  2 Comments

What if m is
mm=[1 2 3 5
1 2 3 9
4 5 6 9
7 8 9 6];
Which row of m, the first or the second, should replace the first row of aa?
In my case there are only one same rows in ‘aa’ and ‘mm’

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2 Answers

Answer by Jos (10584)
on 21 Dec 2017

No need for loops at all! Use both outputs of ismember and replace accordingly
aa = [1 2 3 7
4 5 6 8
7 8 9 9
3 2 3 8
6 5 6 7
7 8 7 9
1 2 3 999];
mm = [1 2 3 5
4 5 6 9
7 8 9 6];
[tf,loc] = ismember(aa(:,1:3),mm(:,1:3),'rows')
% tf indicates which rows in aa are found where (loc) in mm (only for columns 1-3)
aa(tf,:) = mm(loc(tf),:) % replace those rows

  1 Comment

+1 the simplest is the best.

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Answer by KSSV
on 21 Dec 2017
Edited by KSSV
on 21 Dec 2017

aa(1:3,1:3) = mm(1:3,1:3) ;

  1 Comment

Thanks but this codes lost the fourth column values of mm.

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